1. Field of the Invention
This invention relates to an eye direction detecting apparatus for finding an eye direction or a gaze point of a user's eye in a finder system.
2. Description of the Prior Art
U.S. Pat. No. 4,574,314 discloses one kind of conventional eye direction detecting apparatus which detects an eye direction of a user when the user gazes into a view finder.
In U.S. Pat. No. 4,574,314 apparatus has a light source for guiding a light beam to a cameraman's eye and a television camera for receiving a light reflected by a cornea.
An operating circuit in the apparatus finds the coordinates of the gaze point at which a cameraman gazes, and determines which direction the cameraman looks at.
However, the conventional eye direction detecting apparatus is designed without considering the characteristics of the human's eye.
One of the characteristics of an eye is the difference between a visual axis equal to the eye direction and an optic axis. Referring to FIG. 3, which corresponds to FIG. 44 on page 426 of "Behavior Research Methods & Instrumentation 1975, Vol. 7(5)", it can be understood that a visual axis forms an angle of 5.degree..about.7.degree. in general with the optic axis.
Strictly speaking, the above-mentioned detecting apparatus does not detect the eye direction, but the direction of the optic axis. The detected direction is slightly different from the eye direction in which the user looks at.
Another problem is an individual variation. The above-mentioned difference angle is a statistical average. If the individual variation is takes into consideration, the angle would be variously distributed. A distance value k1 is also varied with the individual variation.
Even if, therefore, the difference between the visual axis and the optic axis is optically corrected, the difference owing to the individual variation might remain.
Furthermore, the difference between the two axes is varied when the user wears contact lenses.